Yes, I'm sure it's been done before, but for my sake (as well as those who may be new to shooting); would some of you care to BRIEFLY share your procedure to "zero" your rifle (iron sights / scopes / red dots).

Briefly.
1,Boresight it (with magnifying optics). That will put you on paper without wasting ammo.
2.Benchrest it. Ideally, a vise clamp. Practically, two heavy sandbags will do. Shoot a group of 3.
3.Adjust the sights. Rear goes the same way as you want your hits (higher means up, etc) Front, if necessary, goes the opposite way. Red dot - same as rear irons. Optics - a 4 way adjustment, see manual.
4.Shoot another 3. Repeat until dead on.

If the scope is already on the rifle I will set a target out at 100 yards and see what happens. If it hits the target I will adjust to center the shot group.

If I am putting a scope on a rifle for the first time I will remove the bolt and lay the rifle on sand bags on a table. It is just so it sits still. I will put a target out at 25 yards. I look through the bore to see the target. When the rifle is lined up I adjust the scope to center on the target. I put the bolt back in and fire a round. If it hits anywhere near the center I move the target out further. Eventually I get it out to 100 yards and adjust the scope there. At that point I shoot 3 shot groups. Then I use the center of the three shots as my point of impact. I just keep adjusting the scope until the center of the group is in the center of the target.

Hunting rifles I zero at 200 yards. Everything else I zero at 100.

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Romans 1:16 I am not ashamed of the gospel, because it is the power of God for the salvation of everyone who believes: first for the Jew, then for the Gentile.

i use a combination of C3's method and a bore sighting tool. the boresighter is a valuable tool if you own several rifles with scopes. and can be used to verfy scope adjustments without having to shoot the rifle.

i will mechanically zero the scope. this means if the there are 120 clicks stop to stop i will set the knob at 60 true for elevation and windage. if the rifle has a canted rail, they come in 10,20,30,40 moa ill set the elevation whatever cant value is down.

this will almost certainly get you on paper or very close.

i used to bore sight but dont really bother anymore. if the first shot isnt on paper (extremely rare after a mechanical zero) ill fire one round using the center of each edge as a aimpoint until a shot hits and adjust from there. i like using a 20x20 target.

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"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." — L. Neil Smith

The problem with being stupid is you cannot simply decide to stop doing dumb things...

Use a laser bore sight to get reticle in the ballpark, even down a hallway in your home will suffice to get on paper at the range. Head out, use cheap ammo to walk the bullet to the center, then use desired ammo to zero in.